Electromagnetic inductor



T. WROBLEWSKI ELECTROMAGNETIC INDUCTOR Filed March 26, 1962 ff J2 INVENTOR BY @fk/215% YM July 19, 1966 United States Patent O 3,262,077 ELECTROMAGNETIC INDUCTOR Theodore Wroblewski, Danvers, Mass., assignor to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Filed Mar. 26, 1962, Ser. No. 182,315 4 Claims. (Cl. 336-61) This invention -relates to electromagnetic inductors such as transformers and inductive -reactors comprising a core with one or more coils wound thereon, and has for its object to provide `a strong, rugged inductor -assembly which facilitates mounting of the inductor without increasing the cubic volume required, and which provides for cooling the inductor in operation. Other objects are to provide an electromagnetic .shield for the inductor and to allow for mounting other electrical components.

According to the present invention an electromagnetic inductor comprises a multileg core forming a magnetic circuit, a coil encircling at least one of the core legs, said core having two, spaced, substantially parallel faces and peripheral surfaces extending between the faces, said coil extending a predetermined distance beyond and substantially normal to .said co-re faces, and a magnetic metal sheet of substantial thermal conductivity wrapped around and in thermal contact with said core, said sheet having a mounting portion extending substantially beyond at least one of said core faces.

For the purpose of illustration a typical embodiment of the invention is shown in the accompanying drawing in which:

FIG. l is an isometric view of a transformer;

FIG. 2 is a front elevation;

FIG. 3 is a side elevation;

FIG. 4 is a section on line 4-4 of FIG. 3; and

FIG. 5 is a section on line 5-5 of FIG. 4.

The illustrated transformer comprises two O-shaped core portions 1 surrounding spaces through which one or more coils 2 are wound as shown particularly in FIG. 4 wherein the left core portion is `shown in section and the right co-re portion in elevation.

Each core portion is formed of two laminated members having vertical legs 4 and horizontal legs 6. The members in turn are formed of thin magnetic metal strips 7 of different lengths bent into rectangular C shapes and nested with their ends staggered. Two such laminated C-shaped members are butt-jointed with overlapping ends to form a transformer core portion 1 in which the strips lie in parallel planes laminated outwardly from the coil space.

Prior to the jointing one vertical leg 4 of one core portion 1 is placed back to back with a vertical leg of another and two or more coils are wound around the two vertical legs in the case of a transformer. It will be understood that an inductive reactor may consist of only one O-shaped core, and a single coil wound around one leg of the core.

As illustrated, two core members respectively are buttjointed with the two members on which the coils are wound thereby providing two magnetic flux paths around the O-shaped portions. So assembled the core, per se, is bounded by two parallel faces 8 at the edges of the laminated strips 7 and four outer, peripheral surfaces 9. Two sides of the coil 2 extend outwardly from the core faces 8 `substantially normal t0 the faces a distance equal to the thickness of the coil. Customarily, though not necessarily, the coil is covered with a metallic bell 11 having flanges 15 lying flush against the core faces 8. One of the bells has an opening (21, FIG. 5) through which the coil ends 10 lead to the coil.

According to the invention the transformer is covered 3,262,077 Patented July 19, 1966 by a rectangular magnetic metal sheet 12 wrapped around the core. The overlapping ends 13 of the sheet are joined by .spot welds 14 while the sheet is stressed to insure a good thermal contact with the core portions 1. As indicated by the brackets in FIG. 5, the sheet 12 has a cover -portion 16 in thermal contact with the peripheral portions of the core, and mounting portions 20 at the edges of the sheet extending beyond the 4core faces 8 approximately the same distance as the coil 2 covered by the bells 11. The four flat faces of the sheet 12 thus define a rectangular solid volume not substantially larger than the space which would be allowed for an uncovered transformer.

The cover sheet 12, as so far described, serves to hold the core members tightly together to minimize flux leak age at the butt-joints. Furthermore, the joints and in fact the core 'as a whole is shielded by the sheet so that a minimal amount of flux strays outside the sheet. However, because the four sides of the sheet lie in planes parallel to the laminating strips, the sheet does not bridge the laminations in ysuch a way as to support eddy currents. In these aspects, and others to be described, the sheet substantialy improves the performance of the transformer.

The mounting portions at the edge of the sheet are provided with a plurality of openings 17, preferably through all four faces of the sheet. Bolts, screws or other fasteners passed through the openings of a selected face of the sheet can be used to secure the assembly to the supporting surface of an electrical chassis for example. Alternatively the openings 17 may be used to secure electrical components to the transformer. In either case the sheet extensions 20 afford veasy access to the inner side of the sheet, for example to engage a screw or nut. Additional openings 18 in the extended edges of the sheet are formed by folding tabs 19 inwardly of the sheet into iirm engagement with the anges 15 of the bells 11, thus holding the flanges against the core faces 8 and preventing movement of the core members laterally of the buttjoints.

The openings 17 and 18 provide -a thermal convection path from outside the sheet adjacent the core and coil. The convection path draws cooling air th'rough the openings in a chimney effect which would not exist if the extended sheet edges and openings were not present. The increased sheet Iarea contacting the supporting chassis, and the extended area of the sheet edges affords a considerable increase in heat dissipation by the conduction and radiation from the shield. This coupled with the chimney effect cooling further contributes to the improvement in operation of the transformer.

Thus, while the transformer assembly according to the invention is simple and economical to manufacture, and while the shielding sheet adds negligibly to the weight and volume of the core and coil, greater efficiency and longer life are achieved by the tight thermal contact between the core and the sheet, the increased radiating surface of the sheet, the large `surface a'reas available for conducting heat to a supporting chassis, and the cooling elect of convection currents adjacent the coil and core. High electromagnetic efliciency is afforded by the extended area of the shielding sheet, but in such a way Ias to minimize eddy current loss. The assembly is conveniently mounted at any of four sides and has provision for mounting additional components on its free sides.

It should be understood that the foregoing disclosure is for the purpose of .illustration only and that the present invention includes all modifications which fall within the appended claims.

I claim:

1. An electromagnetic inductor comprising a multileg core comprising at least two butt-jointed members -forming a magnetic cir-cuit, -a coil encircling at least one of the core legs, said core having two, spaced, substantially parallel faces and peripheral surfaces extending between the faces, said coil extending a predetermined distance beyond and substantially normal to said core faces, and a single, magnetic metal sheet of substantial thermal conductivity wrapped around and secured end to end in stressed condition in continuous contact with said peripheral surfaces of said core and providing the sole means of supporting said members and holding said members in tightly butt-jointed relation, said sheet having an integral mounting means forming means to mount the inductor and extending beyond at least one of said core faces substantially the same distance as said coil thereby magnetically to shield the coil.

2. An inductor according to claim l wherein said core comprises two, spaced, substantially parallel faces and peripheral surfaces extending between the faces and said core being formed of laminated thin strips whose laminations lie in planes parallel to said peripheral surfaces, and said sheet is stressed in continuous Contact with said peripheral surfaces thereby to hold `said strips tightly together in butt-jointed relation.

3. An inductor according to claim 1 wherein said core comprises two hollow rectangular portions, each portion comprising at least two butt-jointed members, and each portion having a leg adapted to lie parallel to and in contact with an adjacent leg of the other portion, and said sheet engages the peripheral surfaces of the remaining legs of said portions to hold the portions in said parallel Contact.

4. An inductor according to claim 3 wherein each of said portions `surrounds an inner coil space and comprises a pair of butt-jointed C-shaped members formed of a plurality of parallel magnetic metal strips laminated in planes embracing said inner coil space, and said sheet embraces both said portions to hold said C-shaped members -in tight butt-jointed relation.

References Cited by the Examiner UNITED STATES PATENTS 1,632,101 6/1927 Thordarson 336-84 1,731,894 10/1929 Frisch 336-59 2,548,624 4/1951 Sclater 336-217 X 2,628,342 2/1953 Taylor 336-87 X 2,696,737 12/1954 Mittleman 336-84 X 2,947,957 8/1960 Spindler 336-61 LARAMIE E. ASKIN, Primary Examiner.

JOHN F. BURNS, ROBERT K. SCHAEFER,

Examiners.

W. M. ASBURY, Assistant Examiner. 

1. AN ELECTROMAGNETIC INDUCTOR COMPRISING A MULTILEG CORE COMPRISING AT LEAST TWO BUTT-JOINTED MEMBERS FORMING A MAGNETIC CIRCUIT, A COIL ENCIRCLING AT LEAST ONE OF THE CORE LEGS, SAID CORE HAVING TWO, SPACED SUBSTANTIALLY PARALLEL FACES AND PERIPHERAL SURFACES EXTENDING BETWEEN THE FACES, SAID COIL EXTENDING A PREDETERMINED DISTANCE BEYOND AND SUBSTANTIALLY NORMAL TO SAID CORE FACES, AND A SINGLE MAGNETIC METAL SHEET OF SUBSTANTIAL THERMAL CONDUCTIVITY WRAPPED AROUND AND SECURED END TO END IN STRESSED CONDITION IN CONTINUOUS CONTACT WITH SAID PERIPHERAL SURFACES OF SAID CORE AND PROVIDING THE 